Download Project (1.3 MB)
How does a protein evolve while maintaining its function? Structure/function tests of the sperm tail protein β2-tubulin show that even small changes in the protein render it unable to generate a motile sperm tail, raising the question about how it evolved in the first place. It has not evolved in 60 million years in Drosophila melanogaster. Previously, we identified additive and synergistic amino acid specializations of the β2 protein. Synergism is of particular interest because it makes evolution path-dependent, potentially contributing to the 60-million-year stasis of the β2 protein. Two amino acids, Threonine 55 and Alanine 57, were identified as potentially participating in a β2-specific synergism. Their function depends on amino acid contacts that are only present in β2. Here we test the hypothesis that a third amino acid that is in contact with Thr55 and Ala57 in the folded protein and is also unique to β2, Cysteine 29, completes the synergism, by generating transgenic flies expressing a modified major β1 tubulin containing β2 identity Cys29, Thr55 and Ala57. Spermatogenesis and fertility were assessed in CTA/CTA β2null/β2null flies. CTA can support all post-mitotic tubulin function in the testis, except spermatogenesis. CTA flies generate short, immotile sperm and are sterile. No additional sperm-generating function was provided by Cysteine 29 compared to the β1-β2 construct containing only Thr55 and Ala57.No candidate for sperm generating function is clear in the 11 remaining differences between CTA and β2, indicating that sperm-generating function resides in small epistatic interactions throughout the protein. However, the lack of strong candidates for β2 function raises another possibility; the β1 backbone used in testing for β2 amino acid specializations contains 9+0 specializations that actively generate immotile axonemes. Candidates for such β1 specializations will be identified through bioinformatic comparisons among 9+2 and 9+0 axoneme-generating β-tubulins and tested in transgenic flies.
Primary Advisor's Department
Stander Symposium, College of Arts and Sciences
"How Do Difficult Features Evolve? Test of a Sperm Tail Tubulin Synergism in the Fly D. melanogaster" (2023). Stander Symposium Projects. 2864.